\begin{tikzpicture}[>=Stealth]
    \draw [->] (-2.0,0) -- (3.5,0) node[anchor=north] {$x$};
    \draw [->] (0,-3.5) -- (0,1) node[anchor=east] {$y$};
    \node at (-0.3,-0.3) {$O$};
    \draw (0,0) -- (310:3) node[anchor=north] {$\alpha$的终边};
    \draw [fill=black] (310:2) circle(1pt) node[anchor=west] {$P(x, y)$};
    \node at (0.7,-0.5) {$r$};
\end{tikzpicture}
